"Another ten points from Gryffindor. ...I would expect nothing more sophisticated from you, Ronald Weasley, the boy so solid he cannot Apparate half an inch across a room."
-- Severus Snape (HBP21)

"Wish I could Disapparate like a house-elf. ...I'd have that Apparition Test in the bag."
-- Ron Weasley (HBP21)

Wizards who have come of age can take lessons in Apparition at Hogwarts (HBP17).

A notice for the 12-week course appeared on the Common Room wall in sixth year, along with a sign-up sheet.

Students taking Apparition lessons had to be 17 or to turn 17 by the end of August the following year. Apparition is considered too dangerous for underage wizards, and is tracked by the Ministry using the Trace (DH4).

The lessons began on the first Saturday in February in the Great Hall led by Ministry-Apparition Instructor Wilkie Twycross, a man who seemed perfect for the job of teaching others to travel through thin air: "colourless, with transparent eyelashes, wispy hair and an insubstantial air, as though a single gust of wind might blow him away."(HBP18).

No one can Apparate or Disapparate inside Hogwarts (PA9,PA22), so Dumbledore had to lift the restriction for each one hour class.

Twycross taught the "Three D's" of Apparition: "Destination, Determination, Deliberation." Each student was given a wooden hoop and asked to visualize themselves appearing inside it until they Apparated. Most students including Harry spun in place and got dizzy instead (HBP18).

The first student to Apparate was Susan Bones, but unfortunately she splinched and left her leg behind. The Heads of Houses surrounded her and fixed the problem (HBP18).

By the third class, student nicknames for the instructor included Dog-breath and Dung-head.

The Ministry provided a pamphlet for study called "Common Apparition Mistakes and How to Avoid Them" (HBP22).

The Apparition Test took place in Hogsmeade on April 21st for those who had already turned 17, including Ron Weasley who was struggling with the subject. He and Hermione signed up for extra practice lessons in Hogsmeade.

Snape taunted Ron for his lack of Apparition ability, which made Ron wish he could Apparate and Disapparate as well as a house-elf (HBP21)

Hermione passed the Apparition Test first time, but Ron left half an eyebrow behind and failed (HBP22). It is unknown when and where Ron took the test a second time, or if he ever passed.

Harry, Ernie MacMillan and Draco Malfoy were too young to take the test in April 1997 (HBP22). That would probably include Neville Longbottom as well, since his birthday was a day before Harry's.

According to Draco Malfoy, when the Slytherin named Montague was stuck in the Vanishing Cabinet the year before, he managed to Apparate out even though he had not taken the test (HBP27).

While walking to the portkey to go to the Quidditch World Cup, Amos Diggory said he was looking forward to Cedric taking his Apparition Test (GF6).

Fred and George Weasley passed their Apparition test "with distinction" and enjoyed popping into other people's bedrooms at Grimmauld Place with a loud CRACK! (OP4). Percy Weasley took the test just once and started apparating downstairs every morning, while Charlie Weasley failed his test the first time because he landed on top of a woman who was shopping, five miles south of where he meant to appear (GF6).

Harry never actually took the Apparition Test, although he initiated side-along Disapparition with Dumbledore to get him back from the sea cave when he was weak from Voldemort's Cave Potion (HBP27). Although he was still underage at the point, he was holding Dumbledore's arm and therefore the Ministry would not have Traced him. After he passed his 17th birthday, he apparated at least once alone to Grimmauld Place under the Cloak of Invisibility (DH12), and several times side-along with Hermione and Ron under the Cloak (DH15, DH16, DH19, DH20). The Ministry never knew because by then they were no longer underage so the Trace didn't work.